drm/msm: Fix error handling crashes seen when VRAM allocation fails

If VRAM allocation fails, the error handling path crashes in
msm_drm_uninit(). The following changes are made to fix this:

msm_gem_shrinker_cleanup() is fixed to unregister the shrinker only
if it was init-ed in the first place.

Before calling kms->funcs->destroy(), we check if kms->funcs is also
non-NULL. This is needed for MDP5, since during msm_drm_int(), priv->kms
becomes non-NULL early, but msm_kms_init() is called on it only later
in mdp5_kms_init().

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>
Reviewed-by: Andy Gross <andy.gross@linaro.org>
diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c
index 283d284..192b2d3 100644
--- a/drivers/gpu/drm/msm/msm_gem_shrinker.c
+++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c
@@ -163,6 +163,9 @@ void msm_gem_shrinker_init(struct drm_device *dev)
 void msm_gem_shrinker_cleanup(struct drm_device *dev)
 {
 	struct msm_drm_private *priv = dev->dev_private;
-	WARN_ON(unregister_vmap_purge_notifier(&priv->vmap_notifier));
-	unregister_shrinker(&priv->shrinker);
+
+	if (priv->shrinker.nr_deferred) {
+		WARN_ON(unregister_vmap_purge_notifier(&priv->vmap_notifier));
+		unregister_shrinker(&priv->shrinker);
+	}
 }